Laminated fuel lines usable with fuels containing alcohol (known as gasohol.) are described, for example, in U.S. Pat. Nos. 5,167,259; 5,076,329; 5,038,833 all issued to Brunnhofer. Such laminated fuel lines typically employ a petroleum resistant material such as polyamide, i.e., Nylon 6, Nylon 66, Nylon 11 or Nylon 12.
When a gasohol or alcohol containing fuel is used, in particular, the alcohol component, as well as other fuel components thereof, can diffuse into the polyamide layer causing it to swell. Basically, liquid fuel components can displace plasticizer contained within polyamide resins, creating communication paths for the fuel components to permeate to the exterior of the fuel tube. This problem can be avoided by using metal fuel lines, but metal lines are subject to corrosion and are more difficult to use. In U.S. Pat. No. 4,758,455 issued to Campbell et al., a composite fuel and vapor tube uses an inner liner of a petroleum resistant material such as nylon and a metal strip surrounding and adhered to the outer surface of the liner, and a flexible outer jacket of a halogenated plastic or elastomer. This tube is bendable to an unsupported self sustaining shape and has good heat dissipation properties. Notwithstanding the advantages obtained therefrom, the cost of manufacturing such a construction is relatively expensive.
Aforementioned Brunnhofer contemplates using a barrier layer formed of a copolymer of ethylene and vinyl alcohol with a relatively thicker polyamide layer formed over the inner polyamide layer in attempting to prevent or reduce the alcohol component from permeating through its outer polyamide layer, which can swell the line. Brunnhofer describes that a barrier layer of polyvinyl-alcohol alone is not effective against alcohol. It requires a relatively thick polyamide outer layer in contact with the barrier layer. Specifically, although the inner polyamide layer can undergo swelling, the relatively thicker outer layer that is not directly exposed to the fuel resists the swelling force. Although the polyvinyl barrier may offer some degree of protection against alcohol permeation when properly laminated or bonded to the outer layer, its effectiveness diminishes when the barrier layer becomes delaminated therefrom. U.S. Pat. No. 5,219,003 issued to Kerschbaumer discloses that the adhesion between polyamide and polyvinyl is very slight such that they can delaminate easily. Corrosive chemicals, such salts, which can develop from copper or metal ions present in the fuel, can penetrate between the layers through the fuel ends and delaminate the barrier layer, reducing the vapor barrier effectiveness.
In addition, due to the extreme brittle nature of the polyethylene vinyl alcohol barrier layer, it cannot withstand cold impact tests. In this regard, Kerschbaumer contemplates use of three different polyamide layers, with the barrier layer formed of nylon 66 in attempting form a laminated fuel tube capable of withstanding cold impact tests.
The present invention provides a low cost fuel tube that alleviates the deficiencies of the prior art.